It is well known to use synchronous motors for the operation of pumps, such as pumps for aquariums, pumps for household appliances as, for example, washing machines, dishwashers and more. Synchronous motors comprise a motor body inside which a stator and a rotor are housed. The stator comprises a statoric pack, usually a stack of magnetic laminations, on which one or more electrical windings are wound. The statoric pack has at least two pole pieces inside which a rotor is positioned. Then, the stator forms the inductor of the electric motor.
The rotor usually consists of a permanent magnet of cylindrical shape and constitutes the armature of the electric motor. By feeding the electric windings, a magnetic flux is generated in the statoric pack and, therefore, magnetic poles are generated at the pole pieces that interact with the magnetic field of the rotor, thus causing the rotation of the rotor. The rotor usually is holed in the centre, and inside a shaft is rigidly inserted and fixed. The shaft is supported at its two ends by respective bushes, which are rigidly secured inside cavities formed in the motor body. The impeller of the pump is fixed to one of the two ends of the shaft.
In some motors of the prior art, as shown in FIG. 1, a cylindrical element is used for insulating the statoric part from the rotoric part and, thus, prevents the electric windings of the stator from coming into contact with the liquid to be pumped. In this FIG. 1, a motor pump 10 of the prior art comprising a motor 20 coupled to a pump 50 is shown.
The motor 20 comprises a motor body 22 delimited by walls. By starting from an upper wall 22A of the motor body 22, a cylindrical element 24 extends towards the inside having two ends: a first end 24a facing the wall 22A and open towards the outside, and a second end 24b facing the inside of the motor body 22 and closed by a bottom 26. The cylindrical element 24 thus defines two cavities: a first cavity 28 inside the cylindrical element 24 and a second cavity 30 outside the cylindrical element 24, but contained inside the motor body 22.
A rotor 32 containing a magnet is housed in the first cavity 28, while the stator is housed in the second cavity 30, wherein the pole pieces 34 of the stator have been represented in FIG. 1. The rotor 32 comprises a shaft 36, which is inserted and fixed inside a hole made in the centre of the rotor 32. The shaft 36 has two ends: a first end 36a on which the impeller 52 of the pump 50 is fixed, and a second end 36b housed inside a seat 26a formed on the bottom 26 of the cylindrical element 24. A portion of the shaft 36 between the rotor 32 and the impeller 52 is inserted into a bush 38 wherein the shaft 36 is free to rotate. The bush 38 is fixed by a gasket 40, for example an O-ring, inside the cylindrical element 24.
The pump 50 comprises a pump body 54 mounted onto the motor body 22, and inside the pump body 54 the impeller 52 is housed. By feeding the electric windings of the stator, magnetic poles are generated at the pole pieces 34 which, by interacting with the magnetic field of the rotor magnet 32, put the rotor 32 in rotation and, therefore, also the impeller 52. As can be seen, thanks to the cylindrical element 24, the second cavity 30 that houses the stator is completely closed and, therefore, the electrical windings are completely insulated.
However, this embodiment of the prior art just described has several drawbacks. First of all, the embodiment is quite complex since it is necessary to construct a shaft for transmitting motion from the rotor to the impeller, and it is also necessary to construct a rotor with a hole inside where the shaft is inserted and fixed, and a bush to support one end of the shaft and a housing seat for supporting the other end of the shaft. In addition, once all these elements are constructed, it is necessary to mount them to each other. Then, both the production costs for obtaining the individual pieces, and their assembly, are high. Then, with time and due to wear, it is inevitable that some components may fail and interrupt the correct operation of the motor pump, and also making necessary a cost for the intervention by specialized personnel.
In particular, since the gasket 40 is in contact with the pump body, it is also in contact with the fluid to be pumped, which in some cases is dirty or even aggressive. In fact, the water waste of a washing machine contains chemically aggressive detergents that easily attack and erode the gaskets; therefore, they must be frequently replaced causing evident inconveniences. Moreover, spaces or air chambers are defined between the first cylindrical cavity 28 and the rotor 32, and, more precisely, a first air chamber between the rotor 32 and the bottom 26 of the cylindrical element 24 and a second air chamber between the rotor 32 and the bush 38. Then, the two air chambers are in communication with each other through the space defined between the cylindrical element 24 and the rotor 32.
It was established by the applicant that these air chambers due to (a) the constant starting and stopping of the motor, and (b) the variation of the temperature of the liquid to be pumped (for example, in case of a motor pump for washing machines or dishwashers, the liquid can be either at room temperature or heated), function as minipumps, which suck the liquid contained in the impeller body. But, despite the fact gasket 40 is used, these air chambers are able to suck the liquid contained in the impeller body especially if, as indicated above, it has to be considered that the seals are worn and attacked by the liquid to be pumped.
Therefore, the impurities contained in the liquid, such as detergents, cleansing agents and various impurities in case of motor pumps for washing machines or dishwashers, penetrate inside the cavity, which houses the rotor and, with time, they accumulate and prevent the correct rotation of the rotor inside the cavity, thus causing jamming or irreparable damages to the rotor. This causes issues due to the stopping of the motor and, then, generates a high cost for maintenance or even replacement of the damaged motor pump.
The aim of the present invention is to obviate the drawbacks mentioned above with reference to the cited prior art and, in particular, to avoid a rapid wear of the various components that form the electric motor. Especially, an aim of the present invention is to prevent the rotor functioning incorrectly, or even jamming or failing due to impurities that could penetrate into the cavity.